Solar energy collectors for the heating of water have been made with a grid of substantially parallel pipes mounted in efficient heat conductive relation on a heat-absorbing panel, and the grids are connected by suitable piping to a supply tank containing water to be heated. The grids are also connected to the tank by return piping so that when a pump forces the water from the tank through the grids, the water will collect heat from the absorbers and will return as heated water to the tank for subsequent domestic or other use.
In such installations the solar collectors are usually mounted externally on a building which contains the water storage tank and are thus subject to severe atmospheric conditions, such as freezing temperatures, for example. This has necessitated the use of a suitable antifreeze solution in the water, or in the addition of temperature controlled devices for achieving the drainage of water from the collectors when the temperature reaches a selected low level.
The use of antifreeze in the water is highly undesirable, especially when the water is to be used domestically, because of the toxicity of known antifreeze solutions. Additional means for draining the water from the system is also highly undesirable because of the added cost. Furthermore, such electrical or mechanical means are subject to failure or breakdown and thus cannot provide assurance of continual failsafe operation.
In known solar collector piping circuits a vent valve is used at the high point of the system for allowing air to escape from the piping. However, the system must be operated at a pressure greater than atmospheric pressure and, therefore, any leaks will result in water being deposited undesirably in areas of a building to which access may be difficult.